Wireless communications systems, including cellular phones, paging devices, personal communication services (PCS) systems, and wireless data networks, have become ubiquitous in society. Wireless service providers continually try to create new markets for wireless devices and to expand existing markets by making wireless devices and services cheaper and more reliable. The price of end-user wireless devices, such as cell phones, pagers, PCS systems, and wireless modems, has been driven down to the point where these devices are affordable to nearly everyone and the price of a wireless device is only a small part of the end-user's total cost. To continue to attract new customers, wireless service providers concentrate on reducing infrastructure costs and operating costs while improving quality of service in order to make wireless services cheaper and better.
In order to increase the number of subscribers that can be serviced in a single wireless network, frequency reuse is maximized by making individual cell sites smaller and using a greater number of cell sites to cover the same geographical area. Accordingly, the greater number of base stations increases infrastructure costs, operating costs, and maintenance costs. To offset this increased cost, wireless service providers are eager to implement any innovations that may reduce equipment costs, maintenance and repair costs, and operating costs, or that may increase service quality.
The ability to remotely monitor the RF signals transmitted by the base stations in a wireless network is one important way to maintain a high level of service quality and to reduce maintenance costs. Among the signal parameters that may be remotely monitored are adjacent channel power ratio (ACPR), spectral purity (including in-band and out-of-band spurious components), occupied bandwidth, RHO, frequency error, and code domain power. By remotely monitoring the RF transmitters of a base station from a central location, a wireless service provider can avoid the expense of sending maintenance crews out into the field to test RF transmitters individually. Additionally, a remote monitoring system can detect the failure of an RF transmitter nearly instantaneously.
Conventional wireless networks contain “integrated” base stations in which RF (or radio) functions and non-RF (non-radio) functions are performed within the same physical assembly. RF functions include the transmission, reception, modulation, demodulation, amplification, and filtering of inbound and outbound signals. Non-RF functions include signal processing and switching of low-frequency signals, such as baseband and intermediate frequency (IF) signals. In integrated base stations, the RF signal transmitted by the base station may be directly monitored by built-in test equipment, such as a dedicated test equipment circuit board, installed in the chassis of the base station. The measured RF signal parameters may then be transmitted to a central monitoring facility, such as a mobile switching center, along with the normal voice and data traffic associated with the calls handled by base station.
Recently, however, base stations have been implemented in modular and distributed architectures, rather than as integrated units. In some modular and distributed designs, RF functions are implemented in one module and non-RF functions are implemented in a separate module remote from the RF functions module. One such modular and distributed base station was disclosed in U.S. Provisional Patent Application Ser. No. 60/058228, filed on Sep. 9, 1997, and in U.S. patent application Ser. No. 09/149,168, filed on Sep. 8, 1998, both of which are assigned to Samsung Electronics Co., Ltd., the assignee of the present application. The teachings of U.S. Provisional Patent Application Ser. No. 60/058228 and U.S. patent application Ser. No. 09/149,168 are hereby incorporated by reference into the present application as if fully set forth herein. The Pico-BTS™ system provided by Samsung Electronics Corporation incorporates a modular and distributed base station design in which RF functions are implemented in a radio unit (RU) and non-RF functions are implemented in a separate main unit (MU).
The advantages of a modular and distributed design are many. This design results in a compact RU unit that can be mounted close to the antennas, thereby greatly reducing cable losses in the inbound and outbound RF signals. The separation of RF and non-RF elements results in easier adaption of the modular and distributed design to different RF operating conditions. If the radio unit is upgraded or replaced, it is not necessary to simultaneously upgrade or replace the main unit, and vice versa. For example, if a single non-radio main unit supports three radio units in a three sector antenna system and the main unit is replaced in order to upgrade the signal processing capability of the main unit, the three radio units are not affected. In an integrated base station, the radio units would be discarded along with the outdated main unit.
However, a modular and distributed architecture makes it more difficult to monitor the RF signals transmitted by the radio unit. If the RF test equipment is part of a non-radio main unit, then the RF signal from each radio unit served by the main unit must be forced through a high loss coaxial cable in order to reach the main unit, which makes signal measurements much less accurate. Alternatively, if the RF test equipment is part of the radio unit, then separate RF test equipment must be installed in each radio unit attached to the main unit, which results in redundant test equipment and increased cost.
There is therefore a need in the art for systems and methods for monitoring the RF signals transmitted from one or more radio units in modular and distributed base stations in a wireless network. In particular, there is a need for systems and methods for monitoring the RF signals transmitted by modular radio units that minimizes the amount of test equipment needed without routing the transmitted RF signals through “lossy” cables that reduce the accuracy of signal measurements.